“We found that melt rates are significantly higher than expected across the whole underwater face of the glacier – in some places 100 times higher than theory would predict.” – Rebecca Jackson
Trouble with tidewater glaciers.
The newly observed melt rates are up to two orders of magnitude greater than those calculated by some current predictive models. The findings, published in the July 26 issue of Science, are the first based on direct subsurface measurements of a tidewater glacier and suggest that similar glaciers worldwide may be in far “hotter water” than previously known.
In Earth's Arctic region, vast rivers of ice flow slowly from the ice sheets and ice fields that blanket frozen high-latitude landscapes. Some glaciers are terrestrially bound and often sequestered among high-altitude mountain peaks from the alpine valleys below. Those that meet the sea, however, are called tidewater glaciers. As these bodies of ice push outward into the ocean, their precipitous semi-submerged fronts crumble, or calve, to release a near-constant stream of icebergs into the ocean's currents beyond.
Tidewater glaciers are most common in polar regions, like Greenland, Antarctica and coastal Alaska, where they form the literal boundary between the ocean and the planet's immense reservoirs of frozen freshwater. The nexus between ice and sea makes tidewater glaciers especially influential on the rates of overall ice mass loss and global sea level rise. Furthermore, the large quantities of fresh glacial meltwater discharged into the salty sea have the potential to destabilize or alter global ocean circulation, which is a primary driver of global climate regimes.
Like all of Earth's ice, tidewater glaciers are melting at unprecedented rates, but exact rates are a challenge to ascertain. Unlike alpine glaciers, tidewater glaciers are highly dynamic and can undergo rapid advances and retreats independent of climate changes. Much of the melt attributable to overall ice loss is difficult to measure and occurs either as increased calving or beneath the water. What is known about the dynamics of tidewater glacier melt is predicated upon sparse data and indirect inferences that inform theoretical models of subsurface melt.
Understanding the unique dynamics of tidewater glaciers, particularly as a response to the accelerated warming occurring in high-latitude environments, requires direct observations. However before the survey no direct measurements of underwater melting at tidewater glacier fronts have been made, said David Sutherland, lead author of the study and University of Oregon oceanographer
To address the need for direct submarine melt observations, Sutherland and a team of researchers conducted comprehensive field observations at LeConte Glacier in Southeast Alaska. LeConte, the southernmost tidewater glacier in the Northern Hemisphere, flows from the Stikine Icefield in Southeast Alaska for 21 miles before spilling into a narrow fjord at the edge of the Pacific Ocean. In spite of its size, LeConte's ice flows quite quickly — at a clip of nearly 25 meters per day, or three feet an hour.
Meltwater pulsing out of LeConte Glacier.
Meanwhile, in west Greenland at Store Glacier, another damaged marine-terminating glacier raises alarms.
The clip below is from the Netflix documentary Our Planet. A jaw-dropping video of a Store Glacier calving event.
The cameras catch the moment when a chunk of ice the size of a skyscraper breaks off the Store Glacier in Greenland and tumbles into the ocean. As seabirds circle in the foreground, 75 million tons of crystalline ice cascade into the water below. “Glaciers have always released ice into the ocean,” says narrator David Attenborough. “But now this is happening nearly twice as fast as it did ten years ago.
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